Ultrastructure of the Tabanidae compound eye: Unusual features for Diptera.

The ultrastructure of non-Muscamorpha Diptera is poorly defined. This study is an ultrastructural investigation of the Tabanidae (Diptera) retina, covering 14 species in five genera. The purpose is to identify differences in ultrastructure between tabanids (suborder Brachycera) and the well-known anatomy of muscamorph flies (suborder Cyclorrhapha). Tabanids are observed to have the following features: (i) corneal nipples; (ii) corneal layers; (iii) axial seven-lobed formations in each ommatidium; (iv) closely apposed rhabdomeres distally; (v) rhabdomere twisting only in the proximal ommatidium and (vi) large tracheal air sacs surrounding each ommatidium. Each of these features is described ultrastructurally and discussed with respect to their proposed function.